4. A does 80% of a work in 20 days. He then calls in B and they together finish the remaining work in 4 days. How long B alone would take to do the whole work?
5. A does 60% of a work in 15 days. He then calls B, and they together finish the remaining work in 5 days. How long B alone would take to do the whole work?
6. A and B together do a job in 15 days and A alone could do the same job in 20 days. How many days would B take to do half the job if he worked alone?
7. X, Y and Z can do a piece of work in 30, 40 and 50 days respectively. All three of them began the work together but Y left 4 days before completion of the work. In how many days was the work completed?